With the evolution of more complex infrastructures requiring enhancement, replacement, and expansion in all areas of human occupation, and in particular high-density areas such as cities and suburbs, the ability to accurately map the location of buried conduits, wires and pipelines of various sizes and kinds becomes more pressing, as does the need to document actual as-built underground installations before they are covered so that they can be precisely located at a later date. Worker safety when performing location operations is very important, and workers using various locator devices are killed each year due to lack of visibility to automobiles and other vehicles.
Location operations frequently require the location and identification of existing underground utilities such as underground power lines, gas lines, phone lines, fiber optic cable conduits, cable television (CATV) cables, sprinkler control wiring, water pipes, sewer pipes, etc., collectively and individually herein referred to as “buried objects.” As used herein, the term “buried objects” includes buried and hidden objects, such as objects located inside walls, between floors in multi-story buildings or cast into concrete slabs, for example, as well as objects disposed below the surface of the ground.
The unintended destruction of power and data cables may seriously disrupt the comfort and convenience of residents and bring huge financial costs to business. Therefore human-portable buried object locators (also denoted herein as “utility locators” or just “locators” for brevity) have been developed that sense electromagnetic signals to locate buried utilities such as pipes, conduits, and cables (also known as performing a “locate” or “line trace”). If the buried conductors carry their own electrical signal, they can be traced by detecting the emitted signals at their corresponding frequency. In addition, signals with a known frequency may also be applied to pipes, wires, and cables via a transmitter to enhance the ease and accuracy of the line tracing. This can be done with an electrical clip in the case of a pipe, or with an inductive coupler in the case of a shielded conductor. Sometimes small transmitters known as sondes are used to trace the location of pipes. These are inserted into a pipe and emit electromagnetic signals at a controlled frequency that may be selected for a particular location operation or environment.
Portable utility locators typically carry one or more antennas that are used to detect the electromagnetic signals emitted by buried pipes and cables, and sondes that have been inserted into pipes, typically in the form of magnetic field antennas. The accuracy of portable utility locators is limited by the sensitivity and the configuration of their antennas and associated signal processing circuitry. Signal interference caused by capacitance or inductance within the antenna structures can cause resonance and interference. Additionally, methods of processing signals detected by antennas in portable utility locators by amplifying them and mixing them, may suffer from inefficiencies which include vulnerability to radio-frequency interference (RFI) and electromagnetic interference (EMI), and the introduction of undesirable capacitance and inductance.
Accordingly, there is a need in the art to address the above-described as well as other problems.